Shaving head having separately sprung blades

ABSTRACT

The invention relates to a shaving head for a dry-shaving apparatus comprising a circular shear plate and a cutter member which co-operates with the shear plate and has at least one separately sprung blade the body of which is arranged so as to be movable in an opening in a rotatably drivable blade carrier; in operation the cutting edge of the blade, which edge extends substantially in a radial direction, resiliently engages the shear plate, which is spaced from the blade carrier.

United States Patent 1 Tietjens June 26, 1973 [54] SHAVING HEAD HAVING SEPARATELY 2,280,836 4/1942 Moskovics 30/436 SpR G BLADES 2,289,323 7/1942 Dettle 30/436 inventor: Eduard Willem Tietjens, Drachten,

Netherlands Assignee: ULS. Philips Corporation, New York,

Filed: Feb. 22, 1971 Appl. N0.: 111,502

Foreign Application Priority Data Mar. 25, 1970 Netherlands 7004336 US. Cl. 30/43.6, 30/346.51 Int. Cl B26b 19/14, B26b 19/38 Field of Search 30/-. 3.4, 43.5, 43.6,

References Cited UNITED STATES PATENTS 6/l94i Volz 30/436 Primary Examiner-Othell M. Simpson Assistant Examiner-Gary L. Smith A ttorney-Frank R. Trifari [57] ABSTRACT The invention relates to a shaving head for a dryshaving apparatus comprising a circular shear plate and a cutter member which co-operates with the shear plate and has at least one separately sprung blade the body of which is arranged so as to be movable in an opening in a rotatably drivable blade carrier; in operation the cutting edge of the blade, which edge extends substantially in a radial direction, resiliently engages the shear plate, which is spaced from the blade carrier.

9 Claims, 4 Drawing Figures ILL/I l ///////l SHAVING HEAD HAVING SEPARATELY SPRUNG BLADES Described in French Patent No. 1,188,259 is a known dry shaving apparatus provided with separate springs for the blades in a manner such that during cutting operation or when idling, the cutting edges of the blades are in contact with the shear plate.

As shown in FIGS. 2 and 6 of this prior art reference the perforated shear plate is secured to the upper part of a shaver head housing that generally surrounds the blade carrier and the end of the electric motor output shaft that drives the blade carrier. In operation whiskers extend through hair receiving perforations in the shear plate and are severed when sheared between a cutter blade and the shear plate.

It is an object of the present invention to provide a stable equilibrium between the blade and the shear plate when in engagement during use, which state of equilidependent, as little as possible, on the tolerances.

To ensure a satisfactory shaving effect, dry-shaving apparatus in general requires a close engagement between the blade and the shear plate during the cutting operation, i.e., a stable equilibrium between the blade and the shear plate in this position of engagement, because the entire shaving process takes place in the plane of contact between the blade and the shear plate.

In the known dry-shaving apparatus using rotatably drivable cutting members, stable equilibrium during the cutting operation is usually achieved (a) by maintaining that part of the shear plate (which during the shaving operation is in contact with the cutting edge of the rotating cutting member, and frequently is termed the cutting path of the shear plate) accurately flat, and (b) by using thrust springs for the blades the springs thrust forces sufficient to neutralize any force to be normally expected which tends to distrub this close engagement during the shaving operation.

This maintaining of the cuttinr path accurately flat is a factor which greatly raises the cost of manufacture, and the use of such strong thrust springs entails the disadvantage of the shear plate becoming inconveniently hot owing to the generation of fractional heat with a comparatively more powerful source of energy for driving the cutting member required in relation to the force required for cutting the hairs.

It is a further object of the invention to obviate the above disadvantages with respect to ensuring said state of stable equilibrium. The blade is mounted so as to be tiltable substantially in the radial direction during cutting within a hair is momentarily positioned between a blade and the shear plate, and the blade's cutting edge is resiliently held in engagement with the shear plate during both idling and in the inoperative condition. The invention is characterized in that the center of gravity of the blade is located with respect to the disc-shaped blade carrier, that a centrifugal force which is produced in operation by the rotation and acts through the centre of gravity, produces a restoring force which increases on further deviation and tends to position the body of the blade so that that comparatively weak thrust spring which co-operates with the blade and exerts a force which is directed towards the shear plate and is of the order of magnitude of the inertial forces exerted on the blade but exceeds them, is enabled to achieve a renewed position of engagement between the cutting edge of the blade and the shear plate.

The thrust spring for the blade has a comparatively small force and is required substantially only to ensure correct engagement between the blade and the shear plate in the inoperative condition, while initial deviation from this engagement inthe radial direction during idling or during cutting will usually be corrected at the very beginnigng by a couple which results in a restoring force which increases with increase in deviation.

This means that, although a flat cutting path may be required, there is no need for extreme flatness, since in the case of small irregularities of the cutting path the couple will be capable of preventing significant deviation from the correct position of engagement between the blade and the shear plate. Also, the use for the blade of a thrust spring of comparatively small force permits the use of a power source for driving the rotatable cutting member which is more in accordance with the force required for cutting the hairs than is the base in the known apparatus. Summarizing, it may be stated that according to the invention stable equilibrium between the blade and the shear plate is obtained whice is little dependent on tolerances.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described more fully with reference to the accompanying diagrammatic drawings, in which components not of importance for an understanding of the invention have been omitted, while further advantageous details will become manifest, and in which,

FIG. 1 is a longitudinal sectional view of a shaving head taken in a plane containing the axis,

FIG. 2 shows on an enlarged scale a detail of FIG. 1,

FIG. 3 shows the same detail but with the blade tilted, and

FIG. 4, shows the shaver head in assembled form.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a shaving head 1 which comprises a rotably drivable cutting member 2, which cooperates with a circular rigid or flexible shear plate 3, for example a shear foil within a housing 1 that generally supports the plate. The cutting member 2 is constituted by a disc-shaped blade carrier 4 which has a flat upper surface 5 and a parallel flat lower surface 6, is rotatable about an axis of rotation 7 by a drive shaft 7' (FIG. 4) and is formed with an opening 8 whice extends in the axial direction throughout the entire thickness of the carrier 4 and in which a blade 9 having a cutting edge 10 and a body 11 is mounted movably and substantially radially tiltably.

The cutting edge 10 of the blade 9 is held in engagement with the sjear plate 3 by a thrust spring 12.

In the longitudinal sectional view shown in FIGS. 1 and 2, the body 1 1 of the blade 9 has inward surface 17 and outer surface 13 more remote from the axis of rotation 7 of the blade carrier 4. Surface 13 is accurate, and the blade 9 is proportioned so that the following points of the blade lie substantially in one line: the middle 16 of the are 13, the center of gravity 15 of the blade 9, and the center 14 of the are 13. In the position of the blade in which it is in engagement with the shear plate, this line substantially coincides with the line ofintersection of the longitudinal section shown with the plane containing the axis of the blade carrier 4 and extending at right angles to the plane of the drawing; preferably the center 14 of the are 13 lies between the axis of rotation 7 and that surface 17 of the blade 9 which faces the axis of rotation 7, so that the distance R between the centre 14 of the arc 13 and the middle 16 of the arc l3 considerably exceeds the distance Z between the centre of gravity 15 and the said middle 16. The blade 9 engages the wall of the opening 8 that is remote from the axis of rotation 7, when the blade 9 is urged in operation by the centrifugal force produced. This engagement in a point or along a line only may be regarded as a position of stable equilibrium between the shear plate and the blade, because in the case of a departure from this engaged position, restoring forces will be produced which act on the blade 9 and tend to return it to its initial engaged position. This is illustrated by FIG. 3, which shows the blade 9 in an exaggerated radially tilted position which it is assumed to have up in operation. In this position the acurate surface 13 of the blade 9 engages the remote wall of the opening 8 in a point or along a line 19; a centrifugal force C acts through the center of gravity 15 in a horizontal direction in the plane of the drawing and a reaction force K acts in a direction towards the centre 14' of the are at the point 19. This reaction force may be resolved into vectors V and V V extending horizontally also but in a direction opposite to that of the force C. The forces C and V form a counter-clockwise torque which tends to return the blade 9 to its initial position. The value of this torque increases with increase in the vertical distance between the points 15 and 19, which means that an increasing departure of the blade 9 from its initial engaged position gives rise to an increasing restoring effect. The vector V must naturally be maintained as small as possible, and this is obtainable by keeping the deviation of the curve 13 from a straight line to a minimum, with the restriction that there must be a point or line contact between the surface 13 and the relevant wall of the opening 8. Practice has shown that with a curvature of the arc 13 such that in the initial position its centre lies between the axis of rotation 7 and the surface 17 of the blade 9 facing the axis of rotation 7, restoring forces of acceptable value will be produced.

Although it is far less significant than the torque produced by the centrifugal force and even is substantially negligible, it should be mentioned that, as is'shown in FIG. 3, another counter-clockwise torque is present.

The discrepancy between the torques will be understood by realizing that the disc-shaped blade carrier 4 may be driven at a speed of 4,000 revolutions per minute.

As has been mentioned hereinbefore, the thrust spring 12 has a comparatively small force, because it is only required to overcome the inertial forces exerted on the blade 9 and the friction between the curved surface 13 and the respective wall of the opening 8.

It will now be clear also that in the inoperative condition the center of gracity 15 need not exactly lie in a plane which contains the axis of the blade carrier and extends at right angles to the plane of the drawingg. A requirement is, however, that at any deviation of the blade 9 the center of gravity 15 should remain within that part of the volume of the opening 8 which is bounded by the upper and lower surfaces of the blade carrier 4. This means that a stable equilibrium between the blade and the shear plate is obtainable even with comparatively large manufacturing tolerances, which considerably restricts the cost of manufacture.

Obviously, the invention is not restricted to the embodiment shown in the drawings. For example, the cutting edge 10 of the blade 9 may be slightly inclined with respect to the shear plate 3, and this embodiment in conjunction with the use of a shear plate in the form of a shear foil has yielded highly satisfactory shaving results, as practice has shown.

What is claimed is:

1. A shaving head for use with a dry shaver which includes a housing and a drive means for operating said shaving head, the shaving head comprising, a shear plate supported by the housing, a blade carrier within said housing and rotatably driveable about its axis of rotation by said drive means, the blade-carrier having top and bottom surfaces axially spaced along said axis, and a plurality of openings formed as slots extending between said top and bottom surfaces, each slot having (i) spaced apart sides that defined a planar space generally parallel to said axis, and (ii) inner and outer edge surfaces respectively closer to and remote from said axis of rotation, a plurality of blades each positionable in one of said openings and tippable within said space, each. blade having an upper cutting edge for engagement with said shear plate, and inner and outer edges adjacent to corresponding edges of an associated opening, each blade having a center of gravity, the blade when rotated by said blade carrier subject to centrifugal forces (a) which act at its center of gravity urging it generally outward of said axis, and (b) which form part of a couple urging the blade back to its non-tipped position when it has become tipped in operation, and spring means urging each blade axially toward said shear plate, the spring force being of the same order of magnitude and slightly greater than inertial forces acting on said blade.

2. A shaving head for use with a dry shaver including a housing and drive means for operating said shaving head comprising a blade carrier rotatably driveable about its axis of rotation by said drive means, a shear plate supported by said housing and orientated generally normal to said axis, at least one blade carried by said blade carrier in a plane generally parallel to said shear plate, each blade having a top edge adjacent the shear plate, and inner and outer edges respectively near and remote from said axis of rotation, the carrier having a support edge adjacent and corresponding to said outer edge of said blade, one of said support and outer edges being convex and the other generally flat, the blade having a center of gravity near the center of the blade, whereby the blade when rotated by the bladecarrier has a centrifugal force acting through said center of' gravity urging said center of the blade toward said support edge.

3. A shaving head for use with a dry shaver which includes a housing and a drive means for operating said shaving head, comprising, a shear plate supported by the housing, a blade carrier within said housing and rotatably driveable about its axis of rotation by said drive means, the blade-carrier having top and bottom surfaces axially spaced along said axis, and a plurality of openings formed as slots extending between said top and bottom surfaces, each slot having (i) spaced apart sides that define a planar space generally parallel to said axis, and (ii) inner and outer edge surfaces respectively closer to and remote from said axis of rotation, a plurality of blades each positionable in one of said openings and tippable within said space during cutting operation, each blade having a center of gravity, the blade when rotated by said blade-carrier subject to centrifugal forces which act at its center of gravity urging it generally outward of said axis, and which form a part of a couple urging the blade back to its non-tipped position when it has become tipped in operation, and spring means urging each blade axially toward said shear plate, the spring forcebeing of the same order of magnitude and slightly greater than inertial forces acting on said blade, and wherein said'blade carrier in the location of said openings therethrough, has thickness in the axial direction bounded by top and bottom surfaces of said carrier, said thickness being of sufficient magnitude, such that, during tipping movement of a blade within said opening during operation of the shaver, the

center of gravity of the blades remains within said boundaries.

4. Apparatus according to claim 2 wherein said center of gravity of the blade in its non-tipped orientation blade, the middle of said convex surface, and the center of the arc of said convex surface lie on a straight line.

5. Apparatus according to claim 4 wherein the center of said are lies between said axis of rotation and the inner blade edge.

6. Apparatus according to claim 1 wherein said outer edge of at least one blade is arcuate.

' 7. Apparatus according to claim 1 wherein said slots define radial planes with respect to said axis of rotation.

8. Apparatus according to claim 1 wherein each blade is radially spaced from said axis of rotation.

9. Apparatus according to claim 1 wherein each blade is radially spaced from said axis of rotation and located in a radial plane extending through said axis of rotation. 

1. A shaving head for use with a dry shaver which includes a housing and a drive means for operating said shaving head, the shaving head comprising, a shear plate supported by the housing, a blade carrier within said housing and rotatably driveable about its axis of rotation by said drive means, the blade-carrier having top and bottom surfaces axially spaced along said axis, and a plurality of openings formed as slots extending between said top and bottom surfaces, each slot having (i) spaced apart sides that defined a planar space generally parallel to said axis, and (ii) inner and outer edge surfaces respectively closer to and remote from said axis of rotation, a plurality of blades each positionable in one of said openings and tippable within said space, each blade having an upper cutting edge for engagement with said shear plate, and inner and outer edges adjacent to corresponding edges of an associated opening, each blade having a center of gravity, the blade when rotated by said blade carrier subject to centrifugal forces (a) which act at its center of gravity urging it generally outward of said axis, and (b) which form part of a couple urging the blade back to its nontipped position when it has become tipped in operation, and spring means urging each blade axially toward said shear plate, the spring force being of the same order of magnitude and slightly greater than inertial forces acting on said blade.
 2. A shaving head for use with a dry shaver including a housing and drive means for operating said shaving head comprising a blade carrier rotatably driveable about its axis of rotation by said drive means, a shear plate supported by said housing and orientated generally normal to said axis, at least one blade carried by said blade carrier in a plane generally parallel to said shear plate, each blade having a top edge adjacent the shear plate, and inner and outer edges respectively near and remote from said axis of rotation, the carrier having a support edge adjacent and corresponding to said outer edge of said blade, one of said support and outer edges being convex and the other generally flat, the blade having a center of gravity near the center of the blade, whereby the blade when rotated by the blade-carrier has a centrifugal force acting through said center of gravity urging said center of the blade toward said support edge.
 3. A shaving head for use with a dry shaver which includes a housing and a drive means for operating said shaving head, comprising, a shear plate supported by the housing, a blade carrier within said housing and rotatably driveable about its axis of rotation by said drive means, the blade-carrier having top and bottom surfaces axially spaced along said axis, and a plurality of openings formed as slots extending between said top and bottom surfaces, each slot having (i) spaced apart sides that define a planar space generally parallel to said axis, and (ii) inner and outer edge surfaces respectively closer to and remote from said axis of rotation, a plurality of blades each positionable in one of said openings and tippable within said space during cutting operation, each blade having a center of gravity, the blade when rotated by said blade-carrier subject to centrifugal forces which act at its center of gravity urging it generally outward of said axis, and which form a part of a couple urging the blade back to its non-tipped position when it has become tipped in operation, and spring means urging each blade axially toward said shear plate, the spring force being of the same order of magnitude and slightly greater than inertial forces acting on said blade, and wherein said blade carrier in the location of said openings therethrough, has thickness in the axial direction bounded by top and bottom surfaces of said carrier, said thickness being oF sufficient magnitude, such that, during tipping movement of a blade within said opening during operation of the shaver, the center of gravity of the blades remains within said boundaries.
 4. Apparatus according to claim 2 wherein said center of gravity of the blade in its non-tipped orientation blade, the middle of said convex surface, and the center of the arc of said convex surface lie on a straight line.
 5. Apparatus according to claim 4 wherein the center of said arc lies between said axis of rotation and the inner blade edge.
 6. Apparatus according to claim 1 wherein said outer edge of at least one blade is arcuate.
 7. Apparatus according to claim 1 wherein said slots define radial planes with respect to said axis of rotation.
 8. Apparatus according to claim 1 wherein each blade is radially spaced from said axis of rotation.
 9. Apparatus according to claim 1 wherein each blade is radially spaced from said axis of rotation and located in a radial plane extending through said axis of rotation. 